docs: def write(fn, a, **kwargs):
      """
      Convenience function: Detect file extension and write via Atomistica or ASE.
      Has support for writing LAMMPS data files.
      """
      ext = fn[fn.rfind('.'):].split('@')
      if ext[0] == '.out' or ext[0] == '.dat':
          return write_atoms(fn, a)
      elif ext[0] == '.lammps':
          return write_lammps_data(fn, a, velocities=True, **kwargs)
      elif ext[0] == '.nc':
          return NetCDFTrajectory(fn, 'w').write(a)
      else:
          return ase.io.write(fn, a, **kwargs)